The research project centers on the role of nitric oxide (NO) as a mediator in the process of retinal axon branching and synapse formation in the developing Xenopus visual system. Our lab and others have shown that trophic factors such as BDNF and/or neurotransmitters such as glutamate, have specific effects on axonal branching during development, and there is evidence to suggest that NO may act as a rapid diffusible signal to mediate these effects. I am characterizing the expression of NO in the developing tectum to determine if the molecule is present during the time when axons are arborizing in the optic tectum, and whether its expression correlates with the presence of trophic factor and glutamate receptors. Preliminary data suggests that NO production is correlated temporally and spacially with retinal axon arborization. The second part of the proposal will focus on manipulating levels of NO in the tectum in vivo and measuring parameters of retinal axon branching over 1-2 days using fluorescent photomicroscopy. This will involve administration of NO donors or NOS inhibitors into the tectum, either alone or in combination with BDNF or glutamate analogues and antagonists. Ultimately, I will use caged (inactive) NO that can be activated by photolysis with UV light in specific areas of an axonal arbor at precise times during development of that arbor in order to focally manipulate NO levels. This proposal will allow us to answer complex questions about the role of NO in the process of axonal branching and synapse formation in vivo.